1. Field of the Invention
The present invention relates generally to safety systems for lasers, and more particularly to a method and apparatus for testing laser beam focus and beam alignment prior to operating the laser system, and for taking a safety action if the system is not in proper working condition.
2. Brief Description of the Prior Art
Many types of laser-based devices and systems, having a wide range of applications in fields such as manufacturing, research, communications and medicine have become increasingly well-known and commercially available. The lasers used in many of these devices and systems are often capable of producing energy output that is potentially harmful to both people and equipment.
The potential dangers associated with lasers are several. For example, burns to the skin and clothing or even to nearby equipment, walls or other objects may be sustained if exposed to laser radiation of sufficient energy and for sufficient duration. Further, some forms of laser radiation can damage an unprotected human eye even before it has time to react to the exposure. This may lead to considerable physical damage to the eye, such as cutting or burning, and can also result in temporary or permanent vision impairment or blindness. Depending on the energy, wavelength and focus of the laser radiation, these dangers may be minimal unless the object comes within a few inches of the laser source. At other focal lengths however, the laser radiation may be harmful even at long distances from the source.
Another potential danger associated with lasers is that of chemical vapors, dust or melted liquids that may be formed in the area where the laser interacts with a work surface, such as in laser welding or scribing. The harmful properties of these chemicals may adversely affect nearby persons if inhaled or otherwise transferred to the body.
Because of the potential dangers associated with lasers, a variety of safety devices have been devised to promote safe operation of laser-based equipment. Common forms of safety equipment include items such as safety goggles, workstation enclosures and warning labels, as well as more complex mechanical interlocks and shutter systems designed to disable the laser when safety sensors are triggered. Other systems have been designed to detect and disable rogue laser beams that are reflected, scattered, aimed or otherwise impinge on walls of a room or enclosure containing the laser equipment. One such system includes infrared monitoring of the walls and ceiling to detect heating of the surfaces by stray laser energy. Another system utilizes fluid-filled walls to detect when stray laser energy melts through an enclosure wall allowing the fluid to escape.
Standards have been established to require at least a minimum level of knowledge regarding the safe operation of a laser system to be passed on to a purchaser of such a system. Examples of such standards are those required by the U.S. Department of Health and Human Services Center for Devices and Radiological Health. These standards classify laser products on the basis of the highest level of laser radiation to which human access is possible during operation. Under this system, a class rating I through IV is assigned to denote the risk involved. A Class I system provides the least risk and is one that emissions in the ultraviolet, visible and infrared spectra are at levels below established biological hazard levels. Class II systems are considered a hazard for direct long-term ocular exposure. Class III system emission levels are ocular hazards for direct exposure and may be hazardous to skin at longer exposure times. Class IV systems are the most hazardous and pose a danger to eyes and skin upon direct, as well as indirect exposure such as that resulting from scattered, diffused or reflected radiation.
Ideally, all laser based systems would be operated under a Class I rating in a manner providing the greatest safety to operators and bystanders as well as to nearby equipment and the facility which houses the laser. However, for reasons such as costs and performance requirements, laser systems are often operated at more dangerous classification levels. For example, providing a sealed enclosure for a laser system inside which the laser operation takes place may represent the safest scenario, but may be impractical due to cost and size where the laser system and work piece are large. Further, portable laser systems, by their very nature, may not function optimally with the safety systems available in the art. One instance of this is where a portable laser is used to repair welds on a large, complex structure such as a building. Due to the size of the structure an enveloping enclosure is not feasible. In instances where the laser is to be used on surfaces that are generally planar or have a generally uniform surface topography, a shroud could be utilized to enclose the beam and engage the work piece, thereby preventing escape of harmful radiation. In contrast, where the surface has numerous features such a shroud would be ineffective, because it would be difficult or impossible to sufficiently conform the shroud to the work piece.
Another problem in a laser system is the difficulty in determining the direction in which invisible laser radiation is aimed and what it is striking. Current positioning systems used to direct the laser beam may use gantry systems that move in an X-Y plane, galvanometers, and robotic arms to steer the beam. It may be difficult with these systems to determine if the beam is always aimed at, and focused on, the desired target. If a laser beam is not aimed properly, it may be reflected or scattered off of the target and strike somewhere else, potentially causing damage. Further, if the desired target is misaligned, has a hole in it or is missing altogether, damage to equipment and/or personnel could occur.
Yet another possible hazard derives from the laser system itself. Lasers usually utilize a lens to focus the beam such that the focal point, and greatest intensity, of the beam is located on the surface of the work piece. If the focusing lens is missing or damaged in some way the beam may be unfocused and scattered, refracted or reflected to some other unspecified target. For example, before reaching the focusing lens, laser beams generally have a low divergence and are often expanded with a telescope to lower the divergence even further. Low divergence allows the beam to travel much greater distances before the beam energy becomes too dispersed to cause damage. By placing a focusing lens in the path of the beam the distance the beam must propagate before becoming harmless is greatly diminished.